global. This allows the main __init__ to detect the setup and avoid
attempting to load things that aren't built yet.
This is hackish, but the previously used method would fail if there was an
existing system-wide numpy already installed, for example (which users might
have no control over). There were frequent reports of problems with the
previous method:
- http://projects.scipy.org/pipermail/scipy-user/2007-November/014511.html
- Tickets #561 and #565